Fluid actuated servo-motor control



Feb. 16, 1965 R. w. I 'E GATES ETAL 3,169,451

FLUID ACTUATED sERvo-MOTOR CONTROL Filed Feb. 21, lees s sheets-sheet 1 WITNESSES NVENTORS FDlph W. LeGores Thomas A. Sanobionco Feb. 16, 1965 Filed Feb. 2l, 1963 CONTROL CONTROL FEED BACK R. w. LE GATES ETAL 3,169,451

FLUID ACTUATED SERVOI-MOTOR CONTROL 3 Sheets-Sheet-S FULLY GUVERNING VALVE POSITION FULLY cLosED oPEN Fig.4.

FLUID PRESSURE- P. S. I.

TURBINE SPEED Fig.5

FULL

LLI

LLI

FULLY GovERNlNs VALVE PosmoN FULLY cLosEn OPEN Fig.6.

United States Patent O FLUID ACTUA'IED SERV-MTOR CGNTRGL Ralph W. Le Gates, Thornbury Township, Daim-vare County, and Thomas A. Santobianco, Folsom, Fa.,

assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Feb. 21, 1953, Ser. No. 260,197 7 Ciairns. (Cl. 91-3S5) This invention relates to fluid actuated servo-motors controlled by a pressure responsive relay and having feedback means for restoring the latter to the normal or neutral position.

Servo-motors of the above type ordinarily include an operating piston arranged in an operating cylinder, a pilot valve or relay for controlling the admission and exhaust of motive iluid to the operating cylinder, means for operating the pilot relay to cause movement of the operating piston and follow-up or feedback mechanism actuated by the operating piston to restore the pilot relay to its normal or neutral position.

It is a primary object of the invention to provide` a servo-motor of the above type having an improved feedback arrangement.

Another object of the invention is to provide a servomotor of the above type having a feedback mechanism that is highly sensitive and responsive to movement of the operating piston and operates with a minimum of mechanical friction and Wear.

In accordance with the invention, there is provided a servo-motor of the type described above, having a movable abutment (such as a piston) arranged in a manner to actuate the relay from the neutral position in response to a control iiuid pressure signal, and responsive to an' opposed feedback fluid pressure signal to return the relay to the neutral position. The feedback fluid pressure varies with the position of the actuating piston and is provided by a feedback pressure regulating device connected to a source of high pressure fluid and having means associated with the operating piston for modifying the high pressure fluid in accordance with the position of the operating piston to provide the feedback pressure. In the embodiment shown, the high pressure modifying means comprises movable means forming a free jet of high pressure fluid and a knife-edged cam member carried by the rod of the operating piston. The cam member is arranged to extend across the free jet to a variable degree, in accordance with the position of the actuating piston, thereby to provide the variable feedback pressure.

, The above and the objects are effected by the invention as will be apparent from the following description and claims taken in connection with the accompanying drawings, forming a part of this application, in which:

FIGURE l is a sectional View of a servo-motor embodying the invention;

FIG. 2 is an enlarged. fragmentary sectional view showing the feedback pressure modifying mechanism in the position shown in FIG. l; l

FIG. 3 is a sectional view taken on line III-III of FIG. 2, but with the mechanism in another position; and

FIGS. 4, 5 and 6 are graphs illustrating representative operating characteristics of the servo-motor.

Referring to the drawings in detail, especially FIG. l, there is shown a servo-motor including an operating piston connected to the usual rod 11, the piston being arranged in an operating cyhnder 12 and actuated by motive uid, for example oil, directed thereto from a "icc reservoir 13 of high pressure fluid supplied from a suitable source (not shown) by a conduit 14. Motive fluid is admitted to and exhausted from the operating cylinder at opposite sides of the operating piston 10 by means of a pressure responsive relay or pilot valve 15. As shown, the pilot valve is moved by the opposed forces of a spring .16 and of fluid pressure in a space 17, the iiuid pressure 1n the space 17 being modified by a pressure responsive member 18. The member 18 is provided with an inverted cup valve 19 which covers a drain passage 29 in the relay and regulates iiow therethrough of fluid under pressure being supplied to the space 17 from the reservoir 13 through a suitable orifice 21.

Theupper endV of the relay 15 has an end face exposed to the uid pressure in the interior of the space 17. It the inverted cup valve 19 is moved, thereby modifying the ow area of the annular oriiice formed thereby, it will be apparent that the pressure in the space 17 will change. The arrangement is such that force of the fluid in the space 17 acts on the relay and modifies the force of the spring 16 acting thereon, thereby causing the relay to move in a manner to follow the motion of the member 18.

The pressure responsive device for actuating the pressure responsive member 18 may, for example, comprise a movable abutment or piston 24 arranged in a cylinder 25 and controlled by iiuid pressure applied to the space in the cylinder above the piston 24 by a conduit 26. The conduit 26 is connected to a suitable control device (not shown) which device may be a device responsive to variation in speed due to variation in load on a steam turbine 2S which is to be controlled by the servo-motor, as well known in the art.

In this respect, the steam turbine 2S is provided with the usual governing or steam admission valve structure 29 having a valve member 3) connected to the operating rod 11 of the servo-motor by means of connecting linkage 31.

The speed sensing device (not shown) may be of the type having operating characteristics as illustrated in FIG. 5, hence, by referring thereto, it will be seen that the control fiuid pressure varies from a high pressure value at zero speed on the turbine to a lower value as the speed is increased until, at full speed on the turbine, the control fluid pressure is at its lowest value. In this graph, by way of example, it will be seen that the control pressure varies from a value of 45 p.s.i. at zero speed to a value of about 20 p.s.i. at full speed. As well known in the art, as the load on the turbine increases it is essential to progressively open the governing valve 3) to provide additional motivating steam, as necessary to maintain rated speed with the increased load.

As illustrated in FIG. 4, it will be seen that the governing valve 39 is in the closed position when the control fluid pressure attains its lowest value and moves in the opening direction as the uid pressure increases, until when the control pressure attains its maximum value, the valve is in the fully open position. In this graph, the control pressure is substantially the same as that shown in FIG. 5, that is, the fluid pressure varies from 20 p.s.i. for the closed valve position to 45 p.s.i. for the fully open position.

The specific arrangement of the pilot relay 15 is not important and may be of any suitable well known type. For example, as illustrated, the relay may be provided with suitable annular lands arranged to block and nnblock openings in a valve sleeve member 33 in such a manner that, when the relay 15 is moved upwardly from the neutral position shown, a port 34 connected to the reservoir 13 is disposed in communication with a port 35 communicating with the upper portion of the cylinder 12, while when the relay 15 is moved downwardly from the position shown, a port 36 disposed in communication with the reservoir 13 is disposed in communication with a port 37 communicating with the lower portion of the operating cylinder 12. Also, as well known in the art, when the port 35 is disposed in communication with the port 34, the port 37 is disposed in communication with .the drain passage indicated at 38. Conversely, when the port 37 is disposed in communication with the port 3e, the port 35 is disposed in communication with the drain 3S.

Accordingly, as the operating uid is admitted to one side of the operating cylinder, under control of the relay 15, the duid in the other side of the cylinder is exhausted therefrom to drain, thereby actuating the piston 1i?, while, when the relay is in the neutral position, dow to and from the operating cylinder is terminated, thereby arresting the piston.

In accordance with the invention, there is provided a feedback device or mechanism, generally designated 4t), for providing a feedback fluid pressure signal to the lower space in the cylinder acting in opposition to the control uid pressure in the upper portion of the cylinder 25. The feedback pressure is directed to the lower part of the cylinder 25 by a suitable conduit 41. Hence, the control fluid pressure in the upper portion of the cylinder` 25 is effective to move the pressure responsive piston 24 in downward direction until the opposing force of the feedback pressure is increased to a sufficient value to arrest the motion of the piston 24. As the feedback pressure is further increased, the relay 15 is returned tothe neutral position shown (as hereafter more fully explained).

The feedback mechanism 40, as best seen in FIGS. 2 and 3 includes a cylinder 43 having a movable slide valve member 44 disposed therein and including a pair of spaced annular lands 4S and 46 and an elongated central rod portion 47 extending through the left end of the cylinder. The spaced lands 4S and 46 enclose a space 48 while the land 45 and the right end of the cylinder 43 form a second space or fluid receiver 49. The rod portion 47 is provided adjacent its end with an axially elongated slot Si! and a pair of opposed outlet and inlet nozzles or orifices 51 and 52, respectively, disposed on opposite sides of the slot. The outlet nozzle 51 is disposed in duid communication with the space k48 by an elongated bore 53, while the inlet nozzle 52 is disposed in fluid communication with the space 49 by an elongated bore 54. The slide valve 44 is further provided with a projecting stop portion 56 adapted to abut Ithe right end wall of the cylinder 43 to limit the movement thereof to the right (see FIG. 2) and, in the same manner, the rod portion 47 is provided with an enlarged stop portion 57 adapted to abut the left end wall of the cylinder 43 to arrest movement of the slide valve to the left (see FIG. 3). However, during operation, the slide valve ioats between these two limiting positions and preferably does not move into abutment with either end wall. There is further provided a helical scale spring 59 for biasing the slide valve to the right as illustrated in FIGS. 2 and 3.

The cylinder 43 is provided with pressurized uid from a suitable source (not shown) by a pipetl disposed a1- ways in communication with the space 48, while the space 49 is connected to the conduit 41, as illustrated in FIG. 2. The feedback mechanism 40 is firmly mounted by means of a bracket 61 to the housing 62of the servo-motor so that, in operation, it is stationary with respect to the operating piston rod 11.

The operating rod 11 is provided with a planar knifeedged element or cam member 63 having an inclined edge 64 and disposed in a plane extending parallel to the longitudinal axis of the operating rod 11. The cam 63 is arranged in a manner to be slidably received in the slot As illustrated in FIG. l, the inclined surface of the cam 63 is arranged in such a manner that, at its lower end, it extends only a slight amount past the circumfexa ence of the operating rod 11 and increases in radial specing from the center of the operating rod 11 in upward direction. The cam 63 may be loosely tted in the slot Sil and is employed to variably block and unblock the nozzle 51 in a manner to modify the biasing ect of the scale spring 59 in accordance with the position of the operating piston rod 1L g In operation, when the operating piston 10 is moved from the lowermost position, illustrated in FIG. 1, to the uppermost position, the governing valve 30 is moved to the fully open position and the cani 63 is moved from' the position shown in FIG. 1 to the position shown in FIG. 3.

During such movement of the cam 63, the carri edge 4 progressively recedes (to the left) from the nozzle 51,

thereby tending to unblock ythe nozzle and permit high pressure duid to flow into chamber 49. As the pressure is increased in the chamber 49, the slide valve is urged to the left, compressing the scale spring 59 and moving the nozzle 51 into sufficient blocking relation with the cam 63 `to balance the pressure in chamber 49 against the increased bias of the scale spring. Hence, a's the cam edge progressively tends to recede from the nozzle, the nozzle 51 follows the cam edge. Hence, the slide valve 44 is progressively moved to the left with a following move= ment and is effective to progressively increase the pres sure in chamber 49, until the position shown in FIG. 3 is attained. In this position, the fluid pressure in space 49 attains its highest value, sincel the scale spring is compressed to its maximum operative degree and is effective to balance such highest value..

'Since the pressure in space 4S is always maintained at a high value, some fluid may leak past thevland 46 into the space 66 within which the scale spring 5 9 is disposed and impede its action. Hence, it is desirable to provide a drain outlet 67, as illustrated in FIG. 2. l

When the operating piston rod 11 is returned to the position shown in FIG. 1, the cam 63 is moved downA wardly to its maximum degree with respect to the slide valve 44, thereby (in effect) moving radially outwardly with respect to the axis of the operating rod 11. Ac cordingly, during such movement the cam 63 tends to block the nozzle 51 to a suflicient degree to restrict the How of high pressure fluid from the space 48 into the space 49. As the pressure in space 49 rapidly decays by bleeding through nozzle 52, the spring 59 is effective to move the slide valve 44 to the right with a cam following action until the pressure in space 49 is reduced to a balJ anced Value. In the position shown in FIG. 3, the scale spring 59 is expanded to its maximum operative degree,- hence the feedback uid pressure attains its lowest value.`

For all other positions intermediate the positions shown in FIGS. 2 and 3, the pressure in space 49 will vary between the high and low values, as determined by the degree of compression of the scale spring 59, since the uid pressure in space 49 balances the bias of the spring.

Referring to the graph shown in FIG. 6, it will be seen (by comparing it with FIG. 4) that the feedback mechanism is arranged in such a manner that the feedback pressure signal varies in substantially the same manner and at the same rate as the control signal, that is, when the governing valve 30 is in the fully closed position the feedback pressure is at its lowest value while, when the valve 30 moves in the opening direction, the feedback pressure increases until it attains its maximum value when the valve 3i) is in the fully open position.

The feedback pressure, with the arrangement shown, varies uniformly with the movement of the operating rod 11 and, hence, the governing Valve 36. This characteristic is attained by imparting a rectilinear shape to the edge 64 of the cam 63 and disposing the edge 64 at an angle to the axis of the operating rod 11, so that the slide valve movement is proportional to movement of the actuating rod 11. However, by modifying the contour of the edge.

64, the feedback pressure may be varied in any desirable manner.

In operation, as the servo-motor receives avcontrol pressure signal to move the steam governing valve 30 to a more open position, to maintain rated speed under increased load requirements, the pressure of the fluid admitted to the servo-motor through the conduit 26 will increase, thereby moving the pressure responsive member 18 downwardly and blocking liow of uid through the cup valve 19. Accordingly, the pressure in the space 17 will increase, thereby moving the relay downwardly and permitting motive uid to enter the operating cylinder 12 below the operating piston 10, and thereby moving the operating rod 11 in upward direction to move the governing valve 30 to the more open position. As the operating rod 11 moves upwardly, the feedback pressure signal produced by the feedback mechanism 40 will be progressively increased, as required to balance the control iiuid pressure. Hence, as the operating rod 11 assumes the governing valve opening position required by the control pressure signal, the relay 15 will move upwardly in a following manner as the pressure responsive member 18 is moved upwardly by the increasing feedback pressure. This movement in upward direction by the relay 15 is continued until the relay assumes a neutral position, thereby interrupting the ow from and to the operating cylinder 12 and arresting further motion of the valve 30, as required to maintain turbine speed with the increased load on the turbine. I

Conversely, when the control pressure falls to a lower value, the control pressure in the cylinder above the piston member 24 will decrease, thereby creating an unbalance in the pressure in the cylinder 25. Since the feedback pressure is now higher than the control pressure, the pressure responsive member 18 will move in upward direction until the control pressure signal and the feedback pressure signal are once again in balance. At this time, the operating rod 11 will be moved to a new position corresponding to the control pressure signal.

It will now be seen that the invention provides a simple yet highly effective feedback mechanism for a iluid actuated servo-motor which`mechanism provides a signal that is attained without the use of linkages.

It will further be seen that the invention provides a feedback mechanism wherein the position of the operating piston rod 11 is sensed and a feedback signal provided without direct physical contact of any of the elements of the rod or feedback mechanism, thereby minimizing wear between the relatively mobile rod 11 and the slide valve 44 of the feedback mechanism.

While the invention has been shown in one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof.

We claim as our invention:

1. In a iiuid actuated servo-motor,

an operating cylinder having an operating piston therein,

a movable pressure responsive relay for controlling the admission and exhaust of motive iluid to and from said operating cylinder,

said relay having a neutral position in which the admission and exhaust of the motive lluid is arrested,

means responsive to a variable control uid pressure for effecting movement of said relay from said neutral position,

means rendered effective by movement of said piston for providing a feedback fluid pressure varying in accordance with the position of said piston,

means responsive to said variable feedback pressure for eiecting return of said relay to said neutral position,

said feedback pressure providing means including a uid pressure outlet nozzle,

6 a fluid pressure inlet nozzle disposed* in spaced'registry with said outlet nozzle, a uid receiver communicating with said inlet moule;

means for blocking and unblocking said outlet nozzle in a manner to vary the feedback fluid pressure in said iluid receiver.

2. The structure recited in claim 1 in which said blocking and unblocking means comprises a cam member operatively connected to said piston.

3. In a uid actuated servo-motor,

an operating piston disposed in an operating cylinder and having a piston rod,

a movable pressure responsive relay for controlling the admission and exhaust of motive fluid to and from said operating cylinder,

said relay having a neutral position in which the admission and exhaust of the motive tiuid is arrested,

an abutment movable in response to a variable-control uid pressure for eEecting movement of said relay in a direction away from said neutral position, and

a feedback mechanism for providing a feedback uid pressure varying with the position of said piston rod,

said feedback mechanism including a fluid pressure regulating device having a casing,

a slide valve disposed in said casing and forming therewith a fluid receiving space,

a slide valve being biased in a direction toward said space and having a rod portion extending through said casing,

said rod portion having a slot in its end portion and a fluid outlet nozzle and a fluid inlet nozzle in opposed spaced registry with each other said nozzles being disposed on opposite sides of said slot,

means for delivering a pressurized iuid to said outlet nozzle,

means providing a communication between said inlet nozzle and said fluid receiving space, whereby uid admitted to said inlet nozzle by said outlet nozzle is effective to provide an impact pressure in said uid receiving space, and

a cam member disposed in registry with said slot,

one of said cam members and said pressure regulating device being operatively associated with said piston rod and effective to variably block and unblock said outlet nozzle in accordance with movement of said piston rod, thereby to vary the impact pressure and provide a feedback pressure indicative of the position of said piston rod.

4. The structure recited in claim 3 in which said cam member is carried by said piston rod and movable relative to said pressure regulating device,

said cam having an inclined edge portion arranged to block and unblock said outlet nozzle.

5. In a uid actuated servo-motor,

an operating cylinder having an operating piston therein,

movable pressure responsive means for controlling the admission and exhaust of motive uid to and from said operating cylinder,

means responsive to a variable control fluid pressure responsive controlling means, and

means rendered effective by movement of said operating piston for providing a variable fluid feedback pressure indicative of the position of said piston,

said feedback pressure providing means including a irst movable member defining a uid pressure outlet nozzle, and

a second movable member for blocking and unblocking said outlet nozzle in a manner to vary the fluid feedback pressure,

one of said members being operatively connected to said operating piston.

6. The structure recited in claim 5 in which References Cited in the le of this patent the second member has a cam portion movable trans- UNITED STATES PATENTS versely across said jet of uid. 

1. IN A FLUID ACTUATED SERVO-MOTOR, AN OPERATING CYLINDER HAVING AN OPERATING PISTON THEREIN, A MOVABLE PRESSURE RESPONSIVE RELAY FOR CONTROLLING THE ADMISSION AND EXHAUST OF MOTIVE FLUID TO AND FROM SAID OPERATING CYLINDER, SAID RELAY HAVING A NEUTRAL POSITION IN WHICH THE ADMISSION AND EXHAUST OF THE MOTIVE FLUID IS ARRESTED MEANS RESPONSIVE TO A VARIABLE CONTROL FLUID IS ARRESTED, EFFECTING MOVEMENT OF SAID RELAY FROM SAID NEUTRAL POSITION, MEANS RENDERED EFFECTIVE BY MOVEMENT OF SAID PISTON FOR PROVIDING A FEEDBACK FLUID PRESSURE VARYING IN ACCORDANCE WITH THE POSITION OF SAID PISTON, MEANS RESPONSIVE TO SAID VARIABLE FEEDBACK PRESSURE FOR EFFECTING RETURN OF SAID RELAY TO SAID NEUTRAL POSITION, SAID FEEDBACK PRESSURE PROVIDING MEANS INCLUDING A FLUID PRESSURE OUTLET NOZZLE, A FLUID PRESSURE INLET NOZZLE DISPOSED IN SPACED REGISTRY WITH SAID OUTLET NOZZLE, A FLUID RECEIVER COMMUNICATING WITH SAID INLET NOZZLE, AND MEANS FOR BLOCKING AND UNBLOCKING SAID OUTLET NOZZLE IN A MANNER TO VARY THE FEEDBACK FLUID PRESSURE IN SAID FLUID RECEIVER. 